1. Field of the Invention
The present invention generally relates to repair or circuit modification of microelectronic chips particularly during manufacture. More specifically, chips having conductors, typically copper or aluminum, embedded in organic dielectric layers can be modified after the conductors have been formed. This organic dielectric layer is also variously described in the art by terminology such as low-k dielectric, spin-on glass, or spin-on dielectric.
2. Description of the Related Art
The Focused Ion Beam (FIB) tool is well known in the art for ion milling and has been used for chip analysis, modification, and repair. A typical conventional system utilizes bromine gas and a focused ion beam to selectively mill aluminum lines in a silicon oxide dielectric, a procedure that slices through the conductor to create an electrical open circuit. The complementary procedure of adding conductive material to create shorts or to connect two conductors is done by ion-assisted deposition of a metal such as tungsten from a gaseous metal precursor onto the area to be connected. This conventional method of creating electrical disconnections is not applicable to organic dielectric/metallization schemes because no gas is commercially available that ensures the complete removal of residual metal, such as copper, in the milled area. More important, ion milling utilizes charged ions that impregnate the organic dielectric to defeat electrical isolation.
Conventional methods using FIB milling concern aluminum lines in silicon oxide and does not work for tight pitch copper lines in low-k dielectric materials. Thus, until now no effective method exists to allow circuit modification of chips with organic dielectric layers. The disclosed technique overcomes the above mentioned problems of charged ions and residual metal by using a combination of selective dielectric removal and FIB milling.